Fluid pressure system



Sept. 21, 1943. E. R. FITCH FLUID PRESSURE SYSTEM Fil ed March 19, 1942 EllezyRF ifclz, 77. ,0 @wm Patented Sept. 21, 1943 FLUID PRESSURE SYSTEM Ellery R. Fitch, Elyria, Ohio, assignor to Bendix- Wcstinghouse Automotive Air Brake Company, Elyria, hio, a corporation of Delaware Application March 1-9, 1942, Serial No. 435,403

Claims.

This invention relates to fluid pressure sysg -tems and more particularly to mechanisms for eliminating the difliculties caused by the freezing of moisture in such systems.

In the use of fluid pressure systems-for the operation of vehicle brakes and the like, it has been found heretofore, that considerable mois-' ture couldbe eliminated from the system by providing a plurality of reservoirs arranged to progressively trap moisture from the fluid supficulties under substantially all temperature conplied thereto, the fluid supplied to the first of these reservoirs by the compressor being cooled by means of a suitable radiator for the purpose of condensing such moisture and depositing'it,

in the first reservoir, automatic means controlled by variations of pressure in the system being pro-' vided for automatically discharging a predeter-. mined amount of such condensate from the first,

reservoir, as well as possibly from other reservoirs in the system. It has also been found that some of the detrimental effects of moisture in fluid pressure systems of this type can be eliminated or minimized by adding an anti-freeze medium such as alcohol to the system, but the use of such a medium in connection with devices for automatically discharging condensate from sary waste of the anti-freeze medium. It is likewise known that when operating at relatively'low. temperatures, the use of heat radiators between the compressor and the first reservoir for coolingv when different temperature conditions were encountered; v

It is accordingly an object of the present invention to provide a fluid pressure system for vehicles so constituted as to overcome these difditions encountered in practice.

' A further object of the invention is to provide means for cooling the fluid supplied to the reservoir system by the compressor under normal temperature operating conditions to the end that the vapor reaching the reservoirs will be in the form of liquid condensate easily exhausted therefrom, and at the same time to provide means controlled bythe temperature condition for eliminating this coolingactionand for supplying warm fluid directly to the reservoir system from the compressor under conditions of low temperature operation which would otherwise tend to cause freezing of moisture in the cooling system.

Yet another object of the invention is to provide in a fluid pressure system of the above type, means whereby an adequate supply of fluid for operation-of the system will be maintained at all times at a temperature above freezing, while providing means for cooling the fluid supplied the reservoirs has also resulted in an unnecesthereto sufficiently to eliminate a large portion Y of the water vapor therefrom.

tant parts of the fluid pressure system within the heated body of the vehicle, but-the use of such methods has prevented proper cooling of the fluid for the purpose of condensing the moisture therein, with the result that nearly all the r oisture in the fluid has been retained in susp:nsion and carried over into the operating partsv A further object of the invention is to provide,

in a system having means for condensing moisture from the fluid supplied thereto and exhausting the resultant condensate from the system, means for supplying an anti-freeze mixture to a portion of the system, and means for exhausting condensate from another portion of the system without causing waste of the anti-freeze mixture.

, Other objects and novel features of the invention will appear more fully hereinafter from a consideration of the following detailed description'whentaken in connection with the accompahying drawing illustrating one embodiment of the invention. It is to be expressly understood, however, that the drawing is utilized for purposes of illustration only and is not designed as a definition of the limits of the invention, reference being had for this latter-purpose to the appended claims.

In the drawing, the single figure is a diagrammatic view, partly in section, showing a fluid pressure system illustrative of the present in- V fluid pressure to a reservoir 1 through the medium of a conduit 8 and a control valve H1. The reservoir and valve are also interconnected by a cooling coil on radiator 9, in a manner to be more fully described hereinafter. The second reservoir H is serially connected with the reservoir 1 through a conduit l2, anti-freeze device l3 and a conduit H, the device l3 being of a well-known type and adapted, when filled with alcohol or other anti-freeze medium, to automatically supply alcohol vapor or the like to the fluid flowing to the reservoir through the conduit l4, whenever a flow of fluid from reservoir 1 to reservoir occurs. The second reservoir l likewise supplies fluid to a third reservoir l5 through a conduit I5a, and fluid under pressure is supplied to the brake system from the latter reservoir through conduits l6 and H, the conduit l6 supplying fluid pressure to a. pair of front brake actuators l8 through conduit l9, brake valve 20, conduit 2| and conduit 22, and the conduit controlling the supply of fluid pressure to a pair of rear brake actuators 23 through the medium of a relay control valve 24, conduit 25 and conduit 26. The brake valve 20 is of a well-known type, serving on depression of the pedal 21 to interconnect conduits l9 and 2| to supply fluid pressure to the actuators |8 at a pressure proportional to the amount of depression of the pedal. At the same time, fluid pres sure is supplied to the relay valve from the brake valve through a conduit 28, and serves to actuate the relay valve to establish a connection between conduits l1 and 25, thus supplying a pressure to the rear brake actuators 23 which is at all times substantially proportional to that supplied to the front brake actuators l8 by the brake valve, as will be well understood by those skilled in the art. Means are also provided for controlling the operation of the compressor 6 and for preventing the pumping of fluid thereby when the pressure in the system exceeds a predetermined value, such means including a governor mechanism 29 subjected to the pressure in reservoir l5 through conduit 30 and adapted when this pressure exceeds a predetermined value to connect conduit 36 with aconduit 3| leading to an unloader mechanism on the compressor of well-known design, to actuate the latter and prevent the further pumping of fluid by the compressor until such time as the pressure in the reservoir |5 drops to a lower predetermined value for which the governor 29 can be adjusted, at which time the governor acts to exhaust fluid pressure from conduit 3| to permit the compressor to again resume normal operation.

Reservoirs l and II are provided at their lower portions with automatic pressure operated valves 32, the valve as illustrated sect onally in connection with reservoir including a casing member 33 having a port 34 formed in the upper portion thereof and in communication with the lower portion of the reservoir, the lower end of the port communicating with an enlarged condensate receiving chamber 35, and the latter chamber communicating with atmosphere through an outlet port 36, communicating with an atmospheric discharge port 31. The lower portion of the cas ing is provided with a cavity 38 provided with an atmospheric port 39, and a diaphragm 4|] is clamped against the lower face of the housing by means of a suitable cover plate 4|. The lower port 36 is normally closed by means of a spherical valve 42, the valve being suitably connected to the center of the diaphragm by means of a valve rod 43, a sealing member 44 being mounted in the casing around the valve rod in order to prevent communication between the lower end of the port 36 and the atmospheric chamber 33.

From the foregoing description, it will be apparent that with the valve 42 maintained in the position shown as by means oi. a spring 45 interposed between the casing and the upper face of the diaphragm 40, the escape of fluid from the reservoir through the port 34, chamber 35, port 36 and port 31 will be prevented, while any condensate forming in the bottom of the reservoir will also accumulate in the open port 34, as well as in the enlarged chamber 35. On the application of pressure to the lower side of diaphragm 46, the valve 42 will be forced upward away from the upper end oi port 36 and against the lower end of port 34, allowing the pressure in the reservoir to force the condensate accumulated in the chamber 35 out to atmosphere, through ports 36 and 31, any further escape of fluid pressure from the reservoir being prevented by the action of the valve 42 in sealing the lower end or the port 34. Thus the application of fluid pressure to the lower side of the diaphragm will serve to actuate the valve 42 to permit the discharge of a measured amount of condensate and fluid pressure from the reservoir, and a similar action will take place on release of fluid pressure from the diaphragm 40 prior to the sealing of the upper end 01 the port 36 by the operation of the valve I2.

As heretofore stated, the governor 28 is operative when a predetermined pressure is reached in the reservoir I5 to establish a connection between conduits 30 and 3i to supply fluid pressure to the unloader mechanism of compressor 6, and this same governor action serves to supply fluid pressure to the diaphragms of the automatic drain valves 32 through the medium of conduit 45, normally open valve 46 and conduit 41 in the case of the valve attached to the reservoir H, and through conduits 45 and conduits 48 in the case of the valve attached to reservoir I, the shutoii valve 46 being provided to permit the operator to shut oil the supply of fluid pressure to the valve attached to reservoir under conditions to be hereinafter described.

As stated in the preceding description, the valve In normally serves to connect conduit 8 with the cooling coil 9 in order to permit fluid pressure to flow from compressor 6 to reservoir 1, and as shown in the drawing, this valve includes a casing member 48 divided by suitable partitions into an inlet chamber 49 and a pair of outlet chambers 50 and 5|, chambers 49 and 50 being normally connected through the medium of a hollow plunger 52 slidably mounted in the casing and provided with a bore 53 and ports 54 in the wail of said bore for connecting said ports with the outlet chamber 50. A port 55 is also provided for connecting inlet chamber 49 with outlet chamber 5|, and this port is normally closed by means of a valve member 56 mounted on a valve stem 57 provided at its lower end with a second valve member 58, valve member 56 being normally maintained against the upper end of the port 55 by means of a spring 59 interposed between the easing and the upperside of th valve member 58. The lower portion of the casing 48 is provided withan enlarged cavity 60 having an atmospheric port 6|, the lower end of the cavity being closed by means of a diaphragm 62 suitably clamped to the lower face 01' the casing by means of a cover member 63 and being attached at its center in operative relationship with the plunger 52, the normal position of the diaphragm being such that the upper end of the bore 53 in the plunger 52 is spaced from the lower surface of the valve 58, thus permitting unre tricted communication between conduit; 8 and cooling coil 9 through inlet chamber 49, bore 53, port 54 and outlet chamber 50. Onthe application of fluid pressure to the lower face of the diaphragm 62, it will be apparent that the diaphragm will be forced upward, likewise forcing the plunger 52 upward to a point where the upper end of bore 53 engages the valve member 58, subsequent movement of the plunger in an upward direction serving to move the valve 56 away from the upper end of port 55 to permit communication between inlet chamber 49 and outlet chamber Thus the valve mechanism serves to alternately establish a connection between the inlet chamber 49 and the outlet chamber 50, or to close off such connection and to establish a connection between the inlet chamber and the outlet chamber 5|.

The flow of fluid pressure to the diaphragm is controlled by means of a magnet valve '64 comprising a casing 65 having a solenoid coil 66 suitably mounted therein and adapted on energization to move an armature 61 in a downward direction. The armature is provided with a pair of valves 68 and 69 operatively connected therewith, the armature normally being maintained in the position shown by means of a spring 10 interposed between the lower portion of the casing and the lower face of the inlet valve 69. The casing is divided into an inlet chamber 1 I, an outlet chamber 12 and an exhaust chamber 13, the arrangement of the valves 68 and 69 being such that communication is normally prevented'between the inlet and outlet chambers H and 12 respec tively, and is permitted between outlet chamber 12 and the exhaust chamber 13, movement of the armature downward on energizatlon of the coil serving to disrupt communication between chambers 13 and I2 and to permit communication between chambers 12 and I. The inlet chamber of the valve is supplied with fluid pressure from the reservoir |5 through the medium of conduit 38 and a conduit 14 connected thereto, while fluid pressure is supplied from the valv 64 to the diaphragm 62 of the valve I8 through the medium of a conduit 15 connected at one end to the outlet chamber 12 and at the other end to the cover plate 63 of the valve In, the exhaust chamber 13 of the valve 64 being connected to atmosphere by means of a suitable port 16.

From the foregoing it will be seen that with the valve mechanisms in the positions shown, the conduit 15 will be connected to atmosphere through the valve 64 and no fluid pressure will be supplied to the valve Hi to actuate the valve mechanism to disconnect conduit 8 from the cooling coil 9 and to connect conduit 8 to the outlet chamber 5| of the valve, it being understood that when the latter operation takes place flu d pressure will be supplied to the reservoir 1 from the compressor through conduit 8, outlet chamber 49 of valve I8, port 55, outlet chamber 5| and a c nduit 16 connected to the reservoir 1, the latter action taking place only when the magnet valve 64 is suitably energized.

Since it is desirable to have the coil 9 in the circuit under ordinary temperature condtions, and to eliminate the cooling coil under low temperature conditions tending to cause freezin of condensate therein, means are provided for controlling the energization of the coil 66 of the magnet valve 64 in accordance with temperature changes, such means including a thermostat l1 preferably mounted in or adjacent the second reservoir II in the system. In the present embodiment of the invention, such a thermostat includes a sealed tube 18 mounted in a shouldered boss 19, integral with the reservoir, a block of insulating material 88 being interposed between the upper end of the tube 18 and a nut 8| threadedly received by the boss 19, the nut thus servingto clamp the parts in place and to prevent leakage of fluid pressure from the reservoir past the outer surface of the tube 18. In order to further insure against the escape of fluid pressure at this, point, a sealing member 82 is positioned between the inner portion of the boss 19 and the outer portion of the tube I8 as shown.

A thermostatic element 83 of the bi-metal type is mounted on an extension 84 of the insulating block by means of a suitable bolt 85, and the lower end of the thermostatic element is provided with acontact 86 mounted in electrical engagement therewith and adapted on 'movement of'the thermostatic element to the left to engage a similar contact 81 carried by the projecting member 84. These contacts are normally spaced from each other as shown, contact 81 being connected to one end of the magnet coil 66 by means of a wire 86, and contact 86 being connectedto ground through the medium of thermostatic element 83, bolt and-a wire 89. The circuit from the other side of the magnet coil to ground is completed through a wire 90 connected to one pole of a battery 9| and a wire 92 between the other pole of the battery and the ground connection. Thus movement of the thermostatic element 83 to the left will serve to bring the contacts 86 and 81 together, completing the circuit through the magnet coil 66 and actuating the armature 61 to close valve 68 and open valve 69, thus establishing a connection between conduits 14 and 15 and supplying fluid pressure to the diaphragm 62 of the valve I0 to actuate the valves 58 and 56 to close off communication between conduit 8 and coil 9 and to establish communication between conduit 8 and conduit I6, whereby fluid pressure from the compressor is supplied directly to the reservoir 1 rather than through the cooling coil 9, eliminating the possibility of freezing of condensate therein and clogging of the connection between the compressor and the reservoir.

In order to insure against freezing of moisture in the vital parts of the brake control system, reservoir I5, brake valve 26, relay valve 24 and magnet valve 64 are all located within the relatively warm body of the vehicle, the floor line of the vehicle being indicated by the broken line 93 and the dash line of the vehicle being indicated by the broken line 94. Thus the reservoir I5 and the above described valves are all maintained at a temperature above freezing whenever the vehicle is in operation, and any moisture reaching this part of the system is effectively prevented from freezing. The fluid pressure receiving reservoirs I and H, as well as cooling coil 9, are mounted on the chassis of the vehicle, however, being subjected to atmospheric temperature and to the flow of air thereover due to movement of the vehicle, with the result that the cooling coil 9, as well as the reservoirs and H operate efliciently to cool the fluid supplied thereto by the compressor and to condense and collect moisture carried thereby beforeit reaches the relatively warm reservoir IS, the resulting condensate being automatically discharged from the reservoirs l and II through the operation of the drain valves 32 in response to variations of pressure in the reservoir l5 as hereinbeiore described. Thus, under conditions of moderate temperature operation, the compressor supplies fluid to the reservoirs I and II through the cooling coil 9, no anti-freeze solution being necessary in the device I 3, and both or the valves 32 are effective to automatically drain condensate from the above reservoirs under the control of the governor 29, the reservoirs 1 and II thus being relatively free from condensate at all times and the fluid supplied to reservoir l5 therefrom being in a relatively dry condition.

In the event freezing temperatures are encountered, the device I3 is supplied with a suit able anti-freeze mixture, which is carried into the reservoir II by the movement of fluid in conduits I2 and I4, and since it is desirable that this anti-freeze mixture remain in the system so far as possible, the operator may close the valve 46, thus venting the conduit 41 to atmosphere through a suitable exhaust port 95 provided in the valve, and at the same time cutting ofl! communication between conduits 45 and 41, for the purpose of preventing operation of the valve 32 to discharge condensate from the reservoir ll under any conditions. The valve 32 continues to operate automatically to discharge condensate from the reservoir 1, however, unless actual freezing temperatures are encountered, and in such case the thermostat 17 operates to complete the circuit through the magnet valve 64, thus supplying air to the diaphragm 62 of valve l to actuate the latter valve mechanism to break the communication between conduit 8 and cooling coil 9 and to establish communication between conduits 8 and 16, thus eliminating the cooling action exerted by the radiator on the fluid supplied to the reservoir 1 by the compressor 6 and permitting warm fluid from the compressor to enter the reservoir 1 and prevent the formation of frozen condensate about the upper portion of the valve mechanism 32 which might tend to render this mechanism inoperative.

With the type of operation just described, it will be clear that a greater amount of condensate will be carried over into reservoir ll than would be the case under normal conditions, but freezing of this condensate in reservoir II is prevented by the introduction of the anti-freeze mixture to the reservoir through the action of the device l3, and the resulting mixture of fluid, condensate and anti-freeze mixture will be substantially retained in the reservoir ll, any moisture carried over into the reservoir I being prevented from freezing both by the anti-freeze mixture and by the higher temperature prevailing within the body of the vehicle. In the event the accumulation of anti-freeze mixture and condensate becomes too great in the reservoir l I, this can be readily discharged by manual operation of the valve 46 whenever the pressure in the reservoir 15 is such that the governor 29 operates to establish a connection between conduits 30 and 3| to supply fluid pressure to the unloading mechanism of the reservoir as well as to the actuating diaphragms of the automatic discharge valves 32. In like manner, any condensate collecting within the casings of the valves 20, 24 and G4 is maintained in a liquid condition by the higher temperature prevailing within the body of the vehicle, and due to the construction of these valves, is substantially exhausted to atmosphere therefrom on each operation thereof. The pressure operated control valve It, being directly connected in the discharge line of the compressor, is normally main-' -.again opening the valve 46 to render the valve 32 associated with the reservoir II operative. It is also noted, that while the thermostat 11 may be located at any point subjected to atmospheric temperature, it is preferably located within the reservoir ll so as to accurately read the temperatures prevailing therein. This being the case, it is understandable that when operating at temperatures at or near the freezing point of the condensate, the fluid supplied to the reservoir 1 through the cooling coil 9 may be cooled to a point below the freezing temperature, this fluid also being supplied to the reservoir I l at a temperature below freezing and serving to actuate the thermostat to energize the magnet valve 64 to supply fluid pressure to the valve I 0 to cut out the coil 9 and connect the compressor directly to the reservoir 1, whereupon the temperature of the fluid delivered to the reservoir 1 as well as to the reservoir II will rise to a point suflicient to operate the thermostat in the reverse direction, with the result that the cooling coil 9 will alternately be connected and disconnected from the system, resulting in the maximum cooling of the fluid and condensing of the moisture therefrom under the prevailing temperature conditions, without the possibility of the temperature of the fluid in the above reservoirs dropping to a point where freezing actually occurs. Under conditions of extreme cold weather operation, however, the ther mostat will be operative at all times to energize the above described control mechanism to render the cooling coil ineffective to supply fluid pressure from the compressor to the reservoir 1.

While one embodiment of the invention has been disclosed and described herein, it will be understood that various changes in the component parts of the structures maybe resorted to without departing from the spirit of the invention, as well understood by those skilled in the art. Reference will, therefore, be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

l. The combination with a fluid pressure receiving system having a pair of reservoirs and a compressor for supplying fluid pressure under pressure thereto, of means for serially connecting said reservoirs, means for conducting fluid pressure from the compressor to one of said reservoirs including a heat radiator for cooling the fluid and condensing moisture therefrom, other means for conducting fluid pressure from said compressor to said one reservoir, and means including a valve operable in accordance with variations in temperature in said other reservoir for preventing the flow of fluid pressure from the compressor to said first reservoir through said first named conducting means and for permitting the flow of fluid pressure thereto through said other means when the temperature in said second reservoir is less than a predeter mined value. I r

2. The combination with a fluid pressure system having a compressor and a. pair of reservoirs for receiving fluid pressure therefrom, of means for serially connecting said reservoirs, means including a radiator for conducting fluid pressure from said compressor to one of said reservoirs and for cooling the fluid andcondensing vapor carried thereby, other means for conducting fluid pressure from said compressor to said reservoir, and means controlled by the temperature adjacent the other reservoir for rendering the .flrst means effective for conducting ,fluid pressure from the compressor to the first reservoir when said temperature exceeds a predetermined value and for rendering said other means effective to conduct fluid pressure from the compressor to the said first reservoir when said temperature, drops to a value tending to cause freezing of condensed vapor in said radiator.

3. The combination with a fluid pressure system having a' compressor and a pair of reservoirs for receiving fluid pressure therefrom, of means including a radiator for conducting fluid from said compressor to one of said reservoirs and for cooling the fluid and condensing vapor carried thereby, other means for conducting fluid pressure from said compressor to said reservoir, means controlled by the pressure in said second reservoir for exhausting a predetermined amount of condensate from both said reservoirs when the pressure in said second reservoir exceeds a predetermined value, and means controlled by the temperature in said second reservoir for rendering said vapor condensing radiator inefiective to conduct fluid to said first reservoir from said compressor and for rendering said second named means effective to conduct the fluid to said first named reservoir when said temperature is less than a predetermined value.

4. The combination with a fluid pressure system having a pair of reservoirs and a fluid com pressor for supplying fluid pressure thereto, of means for conducting fluid from the compressor to one of said reservoirs including a radiator for cooling said fluid and condensing vapor carried thereby, means for conducting fluid -from said one reservoir to said other reservoir including means for adding an anti-freeze medium thereto, means controlled by the pressure in said second reservoir for exhausting a predetermined amount of condensate from both reservoirs whenever the pressure in said second reservoir exceeds a predetermined value, and operator controlled means for preventing the operation of the condensate exhausting means associated with said second reservoir when said anti-freeze supplying means is in operation, for preventing the exhausting of said anti-freeze medium from said second reservoir.

5. The combination in a fluid pressure system including a compressor adapted to supply heated fluid under pressure and a pair of reservoirs for receiving said fluid under pressure, of means for serially connecting said reservoirs, means including a connection between said compressor and one of said reservoirs for supplying heated fluid directly thereto, other means connecting said compressor and said one reservoir for substantially r cooling the fluidsupplied thereto and means responsive to the temperature adjacent said other reservoir for rendering the second fluid conducting means effective at relatively highv temperatures and for rendering the first named conducting means effective at relatively low temperatures tending vto. cause freezing of moisture in said fluid cooling means.

6. The combination in a motor vehicle having a chassis portion and a relatively warm enclosed bodyportion associated therewith, of a fluid pres-' sure brake control systemincluding a fluid pressure-receiving reservoir and control valve mechanism for controlling the flow of fluid pressure therefrom to the brakes mounted within said relatively warm body portion, means for supplying fluid pressure to said reservoir including another reservoir mounted on the chassis portion, means for connecting said reservoirs, a compressor for supplying fluid pressure to said second reservoir, aconnection between said compressor and second reservoir including a heat radiator for cooling the fluid supplied thereto by said compressor and for condensing water vapor therein, and means controlled by the pressure in the first named reservoir for exhausting a predetermined amount of condensate from the second reservoir whenever the pressure in the first reservoir exceeds a, predetermined value,

whereby the amount of condensate delivered to said first named reservoir is substantially limited.

7. The combination with a fluid pressure system including a compressor adapted to supply heated fluid under pressure, a plurality of reservoirs for receiving said fluid under pressure and means for serially connecting said reservoirs with the compressor, of means controlled in response to variations of temperature in one of the reservoirs for supplying said heated fluid directly to the first reservoir in said series when said temperature is less than a predetermined value and for cooling the fluid supplied to said first reservoir when said temperature exceeds said predetermined value.

8. The combination with a fluid pressure system including a compressor adapted to supply heated fluid under pressure, a pair of reservoirs for receiving said fluid under pressure and means for serially-connecting said reservoirs with said compressor, of means controlled by the pressure p in one of said reservoirs for automatically ex hausting condensate from the reservoirs, means for normally cooling the supply of fluid delivered to said reservoirs by said compressor whereby condensate is separated from the fluid and collected therein, and means controlled by the tem-' perature in one of the said reservoirs for varying the action in said cooling means whereby the temperature of the fluid delivered to said first reservoir is controlled to permit the collection of a maximum amount of co-ndensatetherein with a minimum amount of freezing thereof.

the temperature of the fluid entering said reservoirs is controlled to prevent freezing of said condensate.

10. The combination with a fluid pressure system including a compressor for supplying heated fluid under pressure, a pair of reservoirs for receiving said fluid under pressure, and means for serially connecting said reservoirs, of means for normally cooling the fluid supplied to said reservoirs whereby condensate carried thereby is condensed and collected in said reservoirs, means controlled by variations of pressure in said reservoirs for periodically exhausting said condensate from said reservoirs, and means operable in response to a predetermined drop in temperature adJacent one of said reservoirs for controlling the action of said cooling means whereby heated fluid is delivered directly to said reservoirs by said compressor for preventing freezing of said condensate.

11. The combination with a fluid pressure system including a compressor adapted to supply heated fluid under pressure, a pair of reservoirs for receiving said fluid under pressure and means for serially connecting said reservoirs, of means associated with one of said reservoirs and said compressor for cooling the fluid supplied to said reservoir and for condensing vapor carried thereby, means associated with said reservoirs and responsive to variations of pressure therein for automatically draining said condensate therefrom, and means controlled by variations of temperature of the fluid in one of said reservoirs for alternately delivering heated fluid or cooled fluid to said one reservoir whereby the maximum amount of condensate is condensed from said fluid and freezing of said condensate in said reservoirs is prevented by the action of said heated fluid.

12. The combination in a fluid pressure brake system including a compressor adapted to supply heated fluid under pressure, a first reservoir subjected to atmospheric temperature for receiving fluid under pressure therefrom, a second reservoir normally maintained at a temperature above freezing for receiving fluid pressure from said first named reservoir, means for normally cooling the fluid delivered to said first named reservoir by the compressor whereby the vapor carried thereby is condensed therefrom and substantially dry fluid is supplied to the second reservoir, means responsive to variation in pressure in said second reservoir for automatically draining condensate from said first named reservoir, and means responsive to atmospheric temperature for controlling the action of said cooling means whereby the fluid supplied to said first named reservoir is normally cooled sufiiciently to deposit condensate therein and whereby under freezing temperature conditions said fluid is supplied to said reservoir at a temperature sufiicient to prevent freezing of said condensate in said reservoir and reservoir connecting means and to permit operation of said automatic drain means.

13. The combination in a fluid pressure brake system including a compressor adapted to supply fluid under pressure, a pair of reservoirs for receiving said fluid under pressure and means for serially connecting said reservoirs, of means associated with said connecting means for supplying an anti-freeze medium to the fluid supplied to said second reservoir, means responsive to variations in pressure in said reservoirs and associated with each reservoir for automatically draining collected condensate therefrom, and manually controlled means for rendering the automatic drain means associated with said second reservoir ineffective whereby the ejection of anti-freeze medium therefrom is prevented.

14. A fluid pressure brake system comprising a compressor adapted to supply heated fluid under pressure, serially connected first, second and third reservoirs for receiving fluid pressure therefrom, the first two of said reservoirs being subjected to atmospheric temperature and the third of said reservoirs being subjected at all times to a temperature above freezing, means for normally cooling the supply of fluid to the first of said reservoirs whereby water vapor carried thereby 29 is condensed and collected in said first and second reservoirs and substantially dry fluid is supplied therefrom to said third reservoir, means responsive to pressure variations in said reservoirs for automatically draining condensate from said first and second named reservoirs, means associated with the connecting means between said first and second named reservoirs for supplying an antifreeze medium to said fluid whereby condensate collected in said second named reservoir and supplied therefrom to said third named reservoir is prevented from freezing, operator controlled means for rendering the automatic drain means associated with second named reservoir ineffective whereby loss of anti-freeze medium therefrom is prevented, and means responsive to the temperature in one of said first named reservoirs for controlling the action of said cooling means whereby the amount of heated fluid supplied to said first named reservoir is sufflcient at all times to prevent freezing of condensate therein and in the means connecting said first and second reservoirs for insuring a supply of fluid to the second reservoir and consequently to the third reservoir at all times.

15. The combination in a fluid pressure system including a compressor adapted to supply heated fluid under pressure, a reservoir for receiving fluid pressure therefrom subjected to atmospheric temperature, a second reservoir subjected to a higher temperature and adapted to receive fluid pressure from said first named reservoir and means for connecting said reservoirs, of means for connecting said first named reservoir and compressor including cooling means for cooling the fluid supplied to said first reservoir and condensing water vapor carried thereby, and means responsive to the temperature in said first named reservoir for controlling the action of said cooling means whereby suflicient heated fluid is supplied to said first named reservoir under all temperature conditions to prevent the freezing of condensate therein and in the first and second reservoir connecting means for insuring a substantially uninterrupted supply of fluid to the second reservoir at all times, the temperature of the second reservoir being suflicient to prevent the freezing of condensate there- ELLERY R FITCH. 

